DESCRIPTION (Adapted from the applicants abstract): This proposal is centered on an investigation of swarm cell differentiation and photoperception by the bacterium Rhodospirillum centenum. This species differentiates from a cell type that has a single polar flagellum used for motility in liquids into a multiflagellated swarm cell which is capable of rapid motility on solid surfaces. The applicant's studies have demonstrated that R. Centenum has a unique mechanism of solid surface perception and subsequent induction of swarm cell differentiation. To study this process, differentiation mutants will be characterized. Motility mutants of the pathogenic bacteria Vibrio cholerae, Salmonella, Campylogbacter jejuni and Helicobacter pylori are know to be significantly less virulent than wild type cells. Swarm cell differentiation mutants of Proteus mirabilis have also been shown to be defective in their ability to infect the bladder or kidney. These results indicate that motility and conversion to swarm cells is an important virulence determinant for some pathogens. Information obtained from this study could therefore have significant practical implications regarding the invasiveness of pathogenic microorganisms. R. Centenum swarm cell colonies also exhibit the remarkable ability to rapidly migrate toward or away from light. Since many mutants obtained in the study of swarm cell differentiation are defective in photosensory perception, this allows us to genetically dissect the process of light perception. Photosynthetic microorganisms are capable of forming massive blooms in aqueous environments where light, temperature, oxygenicity and nutrients are optimal, with several species producing toxic metabolites that can cause deadly threats to humans and animals. Analysis of light-driven colony motility thus has broad implications for the study of photosensory motility exhibited by a variety of motile bacteria.